Free ABO Neuro-Ophthalmology and Orbit Questions and Answers — Questions and Answers
Question 1: A 68-year-old male with long-standing hypertension and diabetes presents with the acute onset of painless, horizontal diplopia. Examination reveals an isolated abduction deficit of the left eye. The remainder of his ocular and neurological exam is normal. What is the most likely diagnosis?
- Cavernous sinus thrombosis
- Myasthenia gravis
- Microvascular sixth nerve palsy (Correct answer)
- Giant cell arteritis
Correct answer: Microvascular sixth nerve palsy
The most common cause of an isolated, non-traumatic sixth nerve palsy in an older patient with vasculopathic risk factors like diabetes and hypertension is a microvascular ischemic event. [8, 27] Cavernous sinus thrombosis would typically present with multiple cranial nerve palsies and proptosis. Myasthenia gravis often presents with ptosis and variable diplopia. Giant cell arteritis is a consideration but is less likely without associated symptoms like headache, jaw claudication, or scalp tenderness.
Question 2: A patient is evaluated for a suspected orbital floor "blowout" fracture after blunt trauma. Entrapment of which extraocular muscle is most commonly associated with restricted upgaze and vertical diplopia?
- Inferior rectus (Correct answer)
- Medial rectus
- Superior rectus
- Lateral rectus
Correct answer: Inferior rectus
The orbital floor is the most common site for a blowout fracture. The inferior rectus muscle and adjacent orbital fat lie directly on the floor and are most susceptible to becoming entrapped within the fracture site in the maxillary sinus. [20, 22] This entrapment mechanically restricts the muscle's ability to relax during upgaze, leading to a limitation of elevation and vertical diplopia. [22]
Question 3: Which of the following visual field defects is most characteristic of a lesion, such as a pituitary adenoma, compressing the optic chiasm from below?
- Homonymous hemianopia
- Central scotoma
- Altitudinal field loss
- Bitemporal hemianopia (Correct answer)
Correct answer: Bitemporal hemianopia
A lesion compressing the optic chiasm, where the nasal retinal fibers from each eye cross, characteristically damages these crossing fibers first. [7] Since the nasal retinal fibers perceive the temporal visual field, this damage results in a bitemporal hemianopia (loss of vision in the temporal half of the visual field for both eyes). [6, 7] This pattern is a classic sign of chiasmal compression. [6]
Question 4: A 28-year-old female presents with a 5-day history of progressively worsening, painful vision loss in her right eye. Her visual acuity is 20/200 OD. Examination reveals a right relative afferent pupillary defect (RAPD) and profound loss of color vision. The optic disc appears normal. What is the most likely diagnosis?
- Non-arteritic anterior ischemic optic neuropathy (NAION)
- Retrobulbar optic neuritis (Correct answer)
- Leber hereditary optic neuropathy (LHON)
- Compressive optic neuropathy
Correct answer: Retrobulbar optic neuritis
This presentation—subacute, painful monocular vision loss with an RAPD and dyschromatopsia in a young adult—is classic for optic neuritis. [19, 25] When the optic disc appears normal, it is termed retrobulbar optic neuritis, as the inflammation is behind the globe. [17, 21] This condition has a strong association with multiple sclerosis. NAION is typically sudden, painless, and occurs in older patients. LHON is painless, and compressive neuropathy is typically gradual and painless.
Question 5: The classic triad of signs for Horner's syndrome consists of ptosis, miosis, and which of the following?
- Proptosis
- Lagophthalmos
- Anhidrosis (Correct answer)
- Lid retraction
Correct answer: Anhidrosis
Horner's syndrome is caused by a disruption of the oculosympathetic pathway. This results in the characteristic triad of ipsilateral ptosis (mild drooping of the upper eyelid due to paralysis of Müller's muscle), miosis (a constricted pupil due to unopposed action of the parasympathetic system), and anhidrosis (decreased sweating on the affected side of the face). [9, 10, 12]
Question 6: A 45-year-old female with Graves' disease presents with proptosis and diplopia. Imaging studies confirm enlargement of the extraocular muscles. Which extraocular muscle is most commonly and prominently affected in thyroid eye disease?
- Inferior rectus (Correct answer)
- Medial rectus
- Superior rectus
- Lateral rectus
Correct answer: Inferior rectus
In thyroid eye disease (Graves' orbitopathy), the extraocular muscles become inflamed and enlarged. The order of frequency of involvement is typically remembered by the mnemonic "IM SLO" (Inferior rectus, Medial rectus, Superior rectus, Lateral rectus, Obliques). Therefore, the inferior rectus is the most commonly affected muscle, often leading to restricted upgaze. [1, 2, 5]
Free ABO Neuro-Ophthalmology and Orbit Questions and Answers
A 68-year-old male with long-standing hypertension and diabetes presents with the acute onset of painless, horizontal diplopia.
Examination reveals an isolated abduction deficit of the left eye.
The remainder of his ocular and neurological exam is normal.
What is the most likely diagnosis?